Update: I just received a very generous offer from Adpinion (a YC company). If your ad is selected then, in addition to the 2-to-3 week period your ad will show on my web site, you'll also get a $40 worth of free advertising on Adpinion's network at large. I think this is a great opportunity to get publicity for free. Don't delay.
Has anyone made an ad-trading site for small web sites? It doesn't even need to be direct swaps: you could make a little marketplace sort of thing (without real money).
I think that's very noble of you, but I have to ask why you're willing to do graphic ads instead of just text ones?
If you're starting a new site, graphic ads can be very jarring to new users, especially if they're just trying to figure out what your site is all about. On the other hand, textual ads can be very subtle, but still useful to any startup - if anything, just to help them out in terms of Page Rank.
I don't know about noble! I just have this big empty space on the right side, and the layout looks unbalanced if I don't fill it. I do use text ads on internal pages, but I prefer images on the home page because they go well with the design. I don't believe it'll have a negative impact on the user experience, otherwise, I wouldn't have done it.
News.YC link exchange sounds like a good idea to me. There might be some competition here, but probably not a ton of overlap. I'd definitely participate with my newest project (soon).
